Rendering images in pygame, blitting ontop of another image

Question

I am currently trying to develop my first game in pyton using the pygame module. I render my Map in two seperate layers, the back- and foreground. If i want to create another pygame.Surface object, where I blit the foreground onto the background. Here are the raw stats of the pygame.Surface objects.

The background:

The foreground:

]

And here is the code for blitting the Images on a new Surface called IMAGE:

self.IMAGE = pygame.Surface((self.width*self.tile_size,self.height*self.tile_size))
self.IMAGE.blit(self.Image_background,(0,0))
self.IMAGE.blit(self.Image_foreground,(0,0))

And also the code for displaying them onto self.WINDOW:

self.WINDOW.blit(self.MAP.IMAGE,(0,0))

Even if i do it like this:

self.WINDOW.blit(self.MAP.Image_background,(0,0))
self.WINDOW.blit(self.MAP.Image_foreground,(0,0))

I will always end up with a blank screen, displaying nothing but the background color. The returned image MAP.IMAGE except has all the needed proporties:

I really appreciate your help! Thank you in advance!

EDIT: Here is my code to update the display:

    def update_display(self):
        pygame.display.update()
        self.WINDOW.fill(BLACK)
        if self.SCREEN == "MENU":
            self.render_menu()
        if self.SCREEN == "NEW MAP":
            self.render_builder()
        pygame.display.flip()

Here is my code for displaying objects (just the map):

def render_builder(self):
        if self.LAYER == self.layers[0]:
            self.display(self.MAP.Image_background,(self.MAP.pos_x,self.MAP.pos_y),scale=False)
        elif self.LAYER == self.layers[1]:
            self.display(self.MAP.Image_foreground,(self.MAP.pos_x,self.MAP.pos_y),scale=False)
        elif self.LAYER == self.layers[2]:
            print(self.LAYER)
            self.display(self.MAP.Image_background,(self.MAP.pos_x,self.MAP.pos_y),scale=False)
            self.display(self.MAP.Image_foreground,(self.MAP.pos_x,self.MAP.pos_y),scale=False)

        self.display(self.right_bar,self.right_bar.topleft,(123,100,123))

Here is my code for displaying anything on the Surface:

    def display(self,what,where=None,color=None,scale=True):
        '''"WHAT" is either a Rect, Surface or String
        If displaying a String, no "WHERE" is needed, otherwise use a Tuple (x,y)
        Default "COLOR" is White, use a tuple to change that (Red,Green,Blue)'''
        if type(what) == pygame.Rect:
            if color:
                pygame.draw.rect(self.WINDOW,color,what)
            else:
                pygame.draw.rect(self.WINDOW,WHITE,what)
        elif type(what) == pygame.Surface:
            if scale:
                what = pygame.transform.scale(what,(self.true_tilesize,self.true_tilesize))
                self.WINDOW.blit(what,where)
            else:
                self.WINDOW.blit(what,where)
        elif type(what) == str:
            if color:
                text_surface = self.FONT.render(what,False,color)
            else:
                text_surface = self.FONT.render(what,False,BLACK)
            text_rect = text_surface.get_rect()
            text_rect.center = where
            self.WINDOW.blit(text_surface,text_rect)